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Mass Extinctions Occur Every 27 Million Years, Study Finds

Scientists from New York University have found that mass extinctions of land-based animals are more predictable than previously thought, and occur roughly every 27 million years in a cycle likely due to our planetary orbit, according to a new study released Thursday.

(CN) — Scientists from New York University have found that mass extinctions of land-based animals are more predictable than previously thought, and occur roughly every 27 million years in a cycle likely due to our planetary orbit, according to a new study released Thursday.

The study, published in the journal Historical Biology, explains how our place in the galaxy has placed us into a cycle of mass extinctions caused by asteroid or comet impacts and subsequent volcanic eruptions.

The Earth has seen a handful of mass extinction events throughout its history from natural disasters, and experts say that without drastic change we are on track to experience another one. 

The most disastrous extinction event of all time was the infamous Cretaceous-Paleogene mass extinction, better known as the death of the dinosaurs. This event eliminated 70% of the planet’s species as a result of an asteroid impact that triggered a series of mega-tsunamis, volcanic eruption, annihilation of land-based resources and eventually an ice age. 

Authors Michael Rampino, a professor in New York University's Department of Biology, Ken Caldeira of the Carnegie Institution for Science and Yuhong Zhu of NYU's Center for Data Science have studied extinction events for years, and their findings have been both groundbreaking and the subject of many debates. 

In their most recent study, the team compared the mass extinctions of land animals to those of marine animals, which experience a loss of approximately 90% of species every 26 million years. Armed with a new approach for statistical analysis, they examined all previous mass extinctions of land animals, including amphibians, reptiles, mammals and birds and discovered a similar cycle occurring every 27.5 million years.

They propose a likely explanation for this has to do with the orbit of our planet in the galaxy. The Earth’s orbit unfortunately lines up with a cycle of comet showers taking place in periodic intervals of 26 to 30 million years. By looking at the ages of impact craters formed after earthly collisions with asteroids and comets, the team discovered a pattern that closely matches the mass extinction cycle not-so-coincidentally.

From an astrophysics perspective, the authors explain that our solar system sits in an orbit that passes through the midplane of the Milky Way galaxy every 30 million years. This area of the galaxy is very densely packed with stars and gas circling in the gravitational pull of a black hole, making it possible for the Earth to experience comet showers and subsequent impacts while passing through. 

The effects of a comet vary depending on the size of the rock, but nevertheless, impacts can wreak havoc on a planet’s environment. The climate can be completely thrown off, resulting in cases of extreme heat and fires, earthquakes and tsunamis ensuing, and dust filling the atmosphere, leaving the surface shrouded in darkness or producing acid rain.

"These new findings of coinciding, sudden mass extinctions on land and in the oceans, and of the common 26- to 27-million-year cycle, lend credence to the idea of periodic global catastrophic events as the triggers for the extinctions," Rampino said in a statement. "In fact, three of the mass annihilations of species on land and in the sea are already known to have occurred at the same times as the three largest impacts of the last 250 million years, each capable of causing a global disaster and resulting mass extinctions."

These impacts have also been found to trigger massive volcanic eruptions called flood-basalt eruptions. After the asteroid impact set off the events leading to the end of the dinosaurs, a series of volcanic eruptions known as the Deccan Traps ravaged the Earth’s surface, releasing enough lava to cover the entire state of Texas. 

Consequently, a long lived debate existed in the scientific community as to whether the asteroid or the volcanic eruptions were the true cause of the death of the dinosaurs. 

"The global mass extinctions were apparently caused by the largest cataclysmic impacts and massive volcanism, perhaps sometimes working in concert," Rampino said.

These eruptions release an immense amount of lava, and have occurred in every land-based mass extinction to date. 

The results of an eruption of this magnitude would have brought fluctuating temperatures, acid rain, destruction of the ozone layer, radiation, and over time a deterioration of the atmosphere’s ability to sustain life. 

In other words, the animals on Earth after an asteroid impact and volcanic eruptions would meet an extremely unfortunate end.

"It seems that large-body impacts and the pulses of internal Earth activity that create flood-basalt volcanism may be marching to the same 27-million-year drumbeat as the extinctions, perhaps paced by our orbit in the Galaxy," Rampino said.

Categories / Environment, Science

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